The present invention relates to a positive resist composition which comprises an alkali-soluble novolac resin and a radiation-sensitive quinonediazide compound and which is suitably used in processing of fine semiconductors integrated circuits.
The fine processing of semiconductor integrated circuits has usually been performed by adopting a lithography process using a resist composition. Among the resist compositions positive working types are used in many cases because of their generally superior resolution. The positive resist compositions comprise generally an alkali-soluble ingredient and a radiation-sensitive ingredient. Specifically, they comprise a novolac resin as an alkali-soluble ingredient and a quinonediazide compound as a radiation-sensitive ingredient. Such a novolac-quinonediazide type positive resist utilizes the fact that the quinonediazide compound, which is alkali-insoluble, is decomposed by the action of radiation to generate a carboxylic group, which makes the compound alkali-soluble.
In recent years, the integrated circuit has become finer and finer with higher integration, and a pattern formation at a sub-micron level has become required. As the result, a positive resist composition having a higher resolution has become desired. For obtaining a finer pattern, so-called chemical amplification resists, which utilize the chemical amplifying effect attained by an acid-generating agent, have also been used in some field. There is still, however, a persistent need for the novolac-quinonediazide type resists.
The resolution of the novolac-quinonediazide type positive resists can be improved by increasing the amount of quinonediazide compound to some extent. However, when the amount of quinonediazide compound is increased too much, the light absorption of the resist becomes very great so that the profile is deteriorated and a rectangular pattern can not be obtained.
The purpose of the present invention is to improve the resolution in the novolac-quinonediazide type positive resists without lowering other resist performances excessively.
As the result of researches, the present inventors have found that the resolution of a novolac-quinonediazide type positive resist composition, which comprises an alkali-soluble novolac resin and a radiation-sensitive quinonediazide compound, can be improved by adding a certain compound. Thus, the present invention was completed.
The present invention provides a positive resist composition which comprises a novolac resin, a radiation-sensitive quinonediazide compound and a thioxanthone compound represented by the following formula (I): 
wherein R1, R2, R3, R4, R5, R6, R7 and R8 independently represent hydrogen, halogen, alkyl, alkoxy, aryl, carboxyl or alkoxycarbonyl.